1. Field of the Invention
The present invention relates in general to magnetic recording and reproduce heads, and more particularly to transducer assemblies having protective surfaces, and to methods of manufacturing such transducer assemblies. The invention has particular relevance to what shall hereinafter be defined as a narrow track head, and to methods of manufacture thereof.
2. Description Relative to the Prior Art
Reference is had to U.S. Pat. Nos. 3,224,073 and 3,761,641 as representative of head manufacture techniques to which the invention is related. As disclosed in each of such patents, in the manufacture of multitrack heads, two sets of slots are sliced into a relatively elongated ceramic block, the first set of slots being fitted with ferrite pieces which are bonded in place. The block and ferrite assembly is then halved longitudinally and, after a gapping substance is deposited on the ends of the exposed ferrite pieces, the two block halves are precisely aligned and bonded back together. Then the second set of slots is fitted with ferrite shield pieces which are bonded to both halves of the ceramic block. The gap between each half of a ferrite piece corresponds to a given information track, the shield pieces being disposed, for example, between pairs of adjacent track-defining ferrite pieces. The whole face assembly is then shaped to optimize the gap cross-sections; and after which the face assembly is fitted with a rear assembly, including magnetic elements, and coils, for completing the magnetic circuits of the track-defining ferrite pieces.
Reference is also had to U.S. Pat. No. 3,710,038 which addresses the long-standing problem of providing a long-lived magnetic video head which withstands a high relative head-to-tape speed and a substantial tape pressure on the head tips. As disclosed in this patent, the appreciable abrasion of the head tips resulting therefrom is is reduced by surrounding the head tips with guard surfaces. By such provision, the tape contact area of the magnetic head is increased and the tape contact force per unit area is correspondingly decreased with consequent extended head tip life. The guard member is formed of a similar ferrite material and adjoins the pole tips. This material provides a tape contact surface having a hardness substantially equal to or a little less than that of the pole tips. If the guard material is incorrectly chosen to have a hardness greater than the ferrite material, the head tips are worn away more than the guard member to draw back its gap surface from the plane of the tape contact surface of the guard member. This results in incomplete contact between the head tips and the magnetic tape and lowers the high frequency component of the output from the magnetic head.
While a head which is manufactured according to the prior art may be functionally acceptable, its structure is such as to leave something to be desired from a manufacturing standpoint: The bonding of the two ceramic block halves requires a painstakingly precise alignment of the gap width of the ferrite pole pieces. Further, in bonding steps subsequent to deposition of the non-magnetic gap, the bonding material may erode into the gap, causing gap length taper, a problem commonly encountered in the glass bonding art. If epoxy is used to bond these surfaces, it becomes difficult in a manufacturing environment to prevent epoxy from collecting on the tape contacting surface of the ferrite pieces. A head manufactured according to this method also has certain performance deficiencies: The geometry of construction constrains the back gap to the same width as the front gap. However, it is desirable to enlarge the back gap area without regard to track width in order to provide a low reluctance path for the magnetic flux and thereby optimize the magnetic circuit.
The current trend toward tape conservation and consequent narrow track widths of 10 mils or even less adds to these manufacturing difficulties by requiring the tape contacting head gap geometry to be extremely narrow. Such narrow ferrite pieces are brittle and subject to edge crumbling both in manufacture and use. Prior art disclosure of guard members or wear shoes may incidentally diminish this problem as to use, but increase the problem as to manufacture, since the brittle ferrite pieces must be additionally subjected to fabrication stresses from attachment of a guard member thereto. The difficulty with using wear shoes or other types of guard members is that they are not directed to the brittleness problem. Wear shoes are primarily adapted to prevent surface abrasion rather than edge crumbling. This means that the emphasis is on increasing the surface area so that the wear shoe shares the abrasive damage of tape contact with the ferrite head tips. As a result, the depth of the head face is more uniformly and slowly eaten away than if only the ferrite tips touched the tape.
The other problem of edge crumbling or, as it is called, "side erosion", is addressed by U.S. Pat. No. 3,584,378. Using a single-track head with a tapered tip, this patent teaches the dipping of such a head into a molten material, such as water glass, and selectively removing thereafter such material from the head to expose the head gap. What remains is a wear-resistant material adhering to the brittle walls of the head. This process, so the patent teaches, is adapted for use with heads which lay down narrow tracks of, for example, 25 mils or even less. However, track widths of 10 mils or less are another matter; such tiny head structures are not amenable, as discrete units, to tapering and dipping without serious danger of damage.